In conventional microscopy, light from a specimen is collected by an objective lens and focused either by an ocular for viewing by eye or by an imaging lens into a detector, for example a charge-coupled device (CCD). A typical arrangement is shown in FIG. 1. This includes an objective lens 2, an imaging lens 4 and a CCD detector 6. Light from a specimen 8 is collected by the objective lens 2 and focused by the imaging lens 4 onto the CCD detector 6. The image recorded by the CCD will represent a thin section 10 of the specimen. Light from all other parts of the specimen will be blurred out.
In a conventional arrangement, the image represents a two-dimensional plane (the X-Y plane) that is perpendicular to the optical axis 12 (the Z-axis) of the objective 2. Sometimes, however, it may be desirable to obtain a three-dimensional image or an image from a plane that is not perpendicular to the optical axis 12 of the objective 2. In either of these cases it is necessary to adjust the focal plane of the objective, so that it collects light from different regions of the specimen. A number of images obtained from different focal planes can then be combined to obtain either a 3D image or a 2D image in a non-perpendicular plane (for example the X-Z plane).